Dispensing guns, and in particular, battery-operated, cordless dispensing guns for dispensing viscous materials such as adhesives, caulking compounds and other sealants included in a collapsible package (i.e., sometimes referred to as a “sausage” or “chub” package) are known in the art. These sausage packages, as the name implies, have a generally elongate, sausage-like shape, and are provided with a flexible, collapsible outer sheath or sleeve that is sealed at its opposed ends for housing the viscous material to be dispensed. In use, one end of the sausage package is either opened or cut to permit the viscous material to be dispensed therefrom. This sausage package is placed in a cylindrical chamber of the dispensing gun and a piston is forced in a forward, or distal dispensing direction to collapse the sheath and force the viscous material out the end of the chamber. The chamber is closed at its dispensing end by a removable cap or closure that includes a dispensing nozzle extending therefrom.
A representative cordless dispenser for dispensing viscous material from sausage-type packages is sold by Albion Engineering Company as its 1000 Series. This caulking gun operates with a 12-volt power supply and includes a motor having a gear for driving a piston rod in a material-dispensing direction. Specifically, the piston rod includes gear teeth that communicate with a pinion gear driven by the motor, whereby operation of the motor results in the pinion gear meshing with the gear teeth of the piston rod to force the piston rod, and the piston attached thereto, in a forward, viscous-material dispensing direction. These cordless dispensers are well known in the art and do not need any further explanation.
A pneumatic prior art caulking gun employing a sausage, or chub package is disclosed in Nealey U.S. Pat. No. 6,223,941 and a hand-operated caulking gun employing a sausage, or chub package is disclosed in U.S. Pat. No. 5,301,835.
In prior art cordless caulking guns, a barrel having a cylindrical chamber is provided for housing the sausage-type package including the viscous material to be dispensed. The dispenser is prepared for operation by retracting the piston rod and the piston attached at a distal end thereof to provide a forward chamber section in the barrel into which the sausage-type package is placed. In some prior art dispensers the piston at the distal end of the piston rod is a plastic member, such as one identified by the trademark TEFLON, and this plastic member has a circular, peripheral edge that is closely adjacent, and preferably rubs against the inner surface of the cylindrical chamber as it is moved in a forward, dispensing direction. This results in the peripheral edge of the piston actually peeling the sausage package liner or casing from the inner wall of the cylindrical chamber of the barrel as the sausage package is being collapsed to dispense the viscous material out of the forward, or distal end of the cylindrical chamber. In this regard, the prior art devices include a closure that is removably attached to the distal end of the cylindrical chamber and a dispensing nozzle extends forwardly from the closure. The dispensing nozzle can be a separate member, or alternatively can be integrally formed as part of the closure. Thus, as the sausage package is collapsed by the forward movement of the piston rod and piston, the viscous material is forced out of the nozzle orifice to a desired location.
In order to ensure that an adequate quantity of viscous material is dispensed, the prior art cordless guns have been designed to continue to apply a force to the sausage package until a predetermined maximum force is detected by the motor, at which time the motor will stop advancing the piston but may continue to push with a predetermined maximum force. Alternatively, upon applying the predetermined maximum force the motor may automatically disengage from the piston rod or shut off. As an example, the Albion 1000 Series caulking gun is designed to automatically shut off when the force detected by the motor reaches a level of approximately 600 pounds. However, the force required to either shut off the motor or stop the motor from continuing to advancing the piston may, in general, be in the range of about 500-2,500 pounds.
In prior art dispensers the pressure build up that ultimately shuts off the motor occurs by the force imposed on the viscous material in the sausage package disposed between the piston at one end and an inner distal surface of the removable closure disposed at the opposed end. The high force build up that is required to shut the motor off can cause an uneven forced distribution about the periphery of the piston, thereby causing excessive wear and/or distortion of the piston edges. Thus, in subsequent uses of the dispenser a slight gap, or a reduction in frictional engagement occurs between the inner surface of the barrel chamber and the distal edge of the piston, which causes a portion of the outer sausage package to be caught, or trapped between the edge of the piston and the inner surface of the chamber as a result of the high force that is created between the piston and sausage package prior to the motor disengaging and/or shutting off. In prior art dispensers the motor either is electronically disengaged when a pre-set maximum force is reached or when the operator releases the motor-actuating button.
When a portion of the sausage package is trapped between the piston and inner surface of the chamber, it becomes extremely difficult to remove a spent sausage package from the gun, even when the cap is removed. First, it is very difficult to get a grasp on the distal end of the sausage package to apply a withdraw force thereto. Second, due to the trapping of a proximal end of the sausage liner between the piston and the inner surface of the chamber, it becomes messy and time consuming to free the dispensed package from the gun in order to permit a new package to be placed in the barrel chamber for subsequent dispensing. Moreover, due to excessive premature wear on the piston, it may become necessary to frequently change the piston, thereby increasing maintenance time and the cost of components.
Therefore, in view of the problems encountered in the prior art devices, a need exists for a more reliable dispenser, and more particularly, a cordless dispenser for sausage packages, which permits the reliable dispensing of viscous material from the sausage package without impairing the ability to easily remove a spent sausage package from the dispenser. It is to such an improved dispenser that the present invention relates.